﻿// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#if DEBUG
using System;
#endif

internal static partial class Interop
{
    internal static partial class Gdi32
    {
        /// <summary>
        ///  Helper to scope selecting a GDI object into an HDC. Restores the original
        ///  object into the HDC when disposed.
        /// </summary>
        /// <remarks>
        ///  Use in a <see langword="using" /> statement. If you must pass this around, always pass
        ///  by <see langword="ref" /> to avoid duplicating the handle and risking a double selection.
        /// </remarks>
#if DEBUG
        internal class SelectObjectScope : DisposalTracking.Tracker, IDisposable
#else
        internal readonly ref struct SelectObjectScope
#endif
        {
            private readonly HDC _hdc;
            public HGDIOBJ PreviousObject { get; }

            /// <summary>
            ///  Selects <paramref name="object"/> into the given <paramref name="hdc"/> using
            ///  <see cref="SelectObject(HDC, HGDIOBJ)"/>.
            /// </summary>
            public SelectObjectScope(HDC hdc, HGDIOBJ @object)
            {
                // Selecting null doesn't mean anything

                if (@object.IsNull)
                {
                    _hdc = default;
                    PreviousObject = default;
                }
                else
                {
                    _hdc = hdc;
                    PreviousObject = SelectObject(hdc, @object);
                }
            }

            public void Dispose()
            {
                if (!_hdc.IsNull)
                {
                    SelectObject(_hdc, PreviousObject);
                }

#if DEBUG
                GC.SuppressFinalize(this);
#endif
            }
        }
    }
}
